Polymer blends

The term polymer blends describes mixtures of polymers that differ from each other in their chemical and physical properties. As in the case of metal alloys, no simple combining of the properties of the individual components occurs, but new properties result. For example, a polymer blend that contains phases of different modules, as compared with conventional polymer organic solids, reacts to mechanical stress with completely different dynamics. Characteristic of polymer blends, apart from the chemical structure of the components, are, in particular, the phase structure and the conformation of the chain molecules in the phases. The thermodynamic interaction of individual chain segments and the molecule conformation can be determined by neutron scattering. The phase structure - the formation of supermolecular structures - is based on separation phenomena in the solution or melt. Hence thermodynamic investigations are intended to shed light on the laws relating to the mixing and separating of high molecular weight polymers. The phase structure of polymer blends is intended to be derived from experimental characteristic data of the individual components. The existence of upper miscibility gaps - corresponding to lower critical solution temperatures - is common for amorphous high polymer blends. This behavior can be appropriately described by an equation of Patterson and Flory. If the changes in entropy and enthalpy are known for the contact of individual segments, the separation temperature for given molar weights can be calculated in advance from characteristic data of the individual components, e.g. thermal expansion coefficients. Polymer blends encompass a broad spectrum of chemical and morphological structures and properties. The formation of interfaces as an adhesion-promoting layer is essential in multiphase polymer blends for technical applications. (orig.)